The ability to stick by your principles is a key requirement for the serious politician.

Saying one thing and then doing another goes down badly with voters, who deplore broken promises and admire leaders who stay true to their principles throughout their careers.

Less than six months into Malcolm Turnbull’s leadership, Australians are entitled to question the Prime Minister’s commitment to the key principles he has ­espoused throughout his many years in public life.

Action on climate change, republicanism and marriage equality used to be priorities for Turnbull. No more. He jettisoned his principles on these issues so he could become Prime Minister. But now there is a new backflip, this time on Turnbull’s claimed interest in the productivity, sustainability and liveability of the nation’s cities.

Last year, as he stalked Tony Abbott, Turnbull incessantly tweeted pictures of himself riding buses, trams and trains to demonstrate his concern about traffic congestion and to highlight how different he was from Abbott, who refused to invest in public transport. Then, on taking the top job, Turnbull appointed South Australian MP Jamie Briggs as minister for cities, promising action to improve the quality of life in cities, which are home to four out of five Australians. However, in the ministerial reshuffle sparked in part by Briggs’s resignation, Turnbull walked away from cities — downgrading the position.

Where it was previously deemed worthy of its own minister, this critical policy area is now being handled by a parliamentary secretary and the Prime Minister has appointed someone who does not live in a major city to fulfil that task. The priority did not even last six months.

Cities are not only places where people live and work, they are also critical to our economic productivity. An Infrastructure Australia report released last year warned that without action, traffic congestion would cost the nation $53 billion a year by 2031.

Tackling the problem requires investment in roads and public transport, as well as promoting ­active transport through the provision of walking and cycling paths. However, Turnbull has failed to reverse Abbott’s decision to scrap important public transport projects such as the Melbourne Metro, Brisbane’s Cross River Rail project, Adelaide’s Gawler Line electrification, and rail and light rail in Perth.

He has continued to promote Abbott’s discredited toll road projects like Melbourne’s East-West Link toll road, which would provide a paltry 45c in public benefit for every dollar invested, and the Perth Freight Link — which has been halted by the ­Supreme Court on environmental grounds.

The government also has failed to re-establish the Major Cities Unit, which was put in place by the former Labor government to drive urban policy and abolished by Abbott.

That means the government has no bureaucratic apparatus for policy implementation. It also has no budget for urban policy issues.

And now it has no minister.

We’ve also heard nothing from the government about the human impacts of traffic congestion.

Because of changes in the pattern of employment growth in the past decade towards inner-city areas and away from the suburbs, millions of Australians can’t find a job near where they can afford to live.

Instead they live in drive-in, drive-out suburbs where they can afford a home but can’t find a job.

They have to commute to the city to work, driving for hours as they watch their quality of life disappearing like the white line in their rear-vision mirror.

It is a tragedy that many working parents spend more time commuting than they spend playing with their children.

The drive-in, drive-out phenomenon is one of the most serious social and economic issues facing modern Australia.

It’s about the economy. But it is also about equity.

Traffic congestion in cities makes it harder for people to access the education and services they need.

It makes it harder for disadvantaged people to improve their circumstances through work or study.

We need more public transport, better roads, greater housing densities along existing public transport routes and improved urban planning and design.

All levels of government need to work together to address this problem, including the commonwealth.

Indeed, as Gough Whitlam said in his famous 1972 election speech: “A national government which has nothing to say about cities has nothing relevant or enduring to say about the nation or the nation’s future.”